Many different types of data storage systems exist and are used to store data cartridges at known locations and to retrieve desired data cartridges so that data may be written to or read from the data cartridges. Such data storage systems are often referred to as autochangers, or "juke box" data storage systems, particularly if they can accommodate a large number of individual data cartridges. The autochanger receives commands from an external source such as a computer system, and in response to those commands can automatically change data cartridges in a cartridge reader. This provides access to multiple data cartridges without the need to manually place them in a cartridge reader.
A typical autochanger system may include one or more different types of cartridge receiving devices for holding the various data cartridges. For example, one type of cartridge receiving device may comprise a cartridge storage rack or "magazine" while another type of cartridge receiving device may comprise a cartridge read/write device. The cartridge storage racks or magazines serve to provide storage locations for the data cartridges and are often arranged so that they form one or more rows, although other configurations are possible. The cartridge read/write device may be located at any convenient location within the data storage system.
The autochanger may also be provided with a moveable cartridge picker assembly or "picker" for transporting the data cartridges between the various cartridge receiving devices, e.g., between the cartridge storage racks and the cartridge read/write devices. A typical cartridge picker assembly or picker may also be provided with a cartridge plunge mechanism or "thumb" assembly for engaging the various data cartridges contained in the cartridge receiving devices and for drawing them into the picker. A picker positioning system associated with the cartridge picker assembly may be used to move the cartridge picker assembly along the various cartridge receiving devices.
Autochangers of the type described above are usually connected to a host computer system which may be used to access or store data on the data cartridges. For example, if the host computer system issues a request for data contained on a particular data cartridge, a control system associated with the data storage system will actuate the picker positioning system to move the picker assembly along the cartridge storage racks until the picker assembly is positioned adjacent the desired data cartridge. The cartridge plunge mechanism or "thumb" assembly associated with the picker assembly may then remove the data cartridge from the cartridge storage rack and draw it into the picker assembly. The picker positioning system may then be actuated to move the picker assembly to the appropriate cartridge read/write device. Once properly positioned adjacent the cartridge read/write device, the thumb assembly may insert the selected data cartridge into the cartridge read/write device so that the host computer may thereafter read data from or write data to the data cartridge. After the read/write operation is complete, the thumb assembly may be actuated to remove the data cartridge from the cartridge read/write device. The picker assembly may thereafter return the data cartridge to the appropriate location in the cartridge storage rack.
It may be advantageous to connect multiple autochanger modules in order to increase the total storage capacity of the system. In one system, multiple autochanger modules have been interconnected in a vertical stack. A single picker assembly is provided for the multiple autochanger modules, and the autochanger modules are configured so that the picker assembly may be moved vertically between the autochangers as well as horizontally inside a single autochanger. The picker assembly may thus access a data cartridge from any autochanger and place it in any cartridge read/write device in the stack of autochanger modules. The total storage capacity of the system is thereby increased, as well as the number of cartridge read/write devices which may be simultaneously accessed. There are several advantages of creating an autochanger stack over simply connecting multiple individual autochangers to a network. First, the cost of an autochanger stack is less than the equivalent number of individual autochangers, since only one picker assembly is needed, and individual housings are not needed. Furthermore, the computer system only needs to address one device with a stacked autochanger, rather than multiple devices. This allows all cartridge read/write devices in the autochanger stack to access any data cartridge from any level in the stack.
However, currently known vertical stacking systems for autochangers are not without their problems. A large number of electrical connectors are required between the autochanger modules in the autochanger stack. Aside from the data and address bus cables which must be connected to each cartridge read/write device in each autochanger, many control cables must be connected to each autochanger. For example, in an autochanger stack with eight autochangers, each autochanger may have two drawers for inserting magazines or read/write devices. Three sensors are connected at each level to determine the position of the drawers, requiring 24 cables between the eight autochanger modules in the stack. Additional cables may be required to eject or load a data cartridge, to read the status of an autochanger after an operation, or to control indicator lights on the front panels of the autochangers. The many control functions in the stacked autochangers therefore require a large number of electrical connectors, increasing the cost of the stacked autochanger system and complicating assembly and maintenance. Large and bulky ribbon cables also require a large amount of space, increasing the size of the stacked autochanger system. This adds to the complexity of the autochanger stack, making it difficult to connect each cable to the appropriate autochanger module in the stack.
Consequently, a need exists for an improved system for stacking autochangers. In particular, a need exists for a system enabling stacking of autochanger modules with a reduced amount of cabling between modules.